Field of the Invention
The present invention relates to a heater and a honeycomb structure including the heater.
Description of the Related Art
Regulations about the harmful materials, such as HC, CO, NOx, and PM exhausted from internal combustion engines, such as a gasoline engine and a diesel engine, have been reinforced on a global scale, but regulations about CO2 emissions in addition to the above-mentioned emissions also have been reinforced for the current global warming issue and there is a demand on the improvement of fuel efficiency. For this reason, the improvement of the thermal efficiency of an engine has been examined to improve the fuel efficiency of an automotive gasoline engine and an automotive diesel engine.
In the past, exhaust gas has been purified using a honeycomb structure coated with a catalyst. However, since the temperature of exhaust gas of the engine is lowered when the thermal efficiency of the engine is improved, there is a problem in that the temperature of an exhaust gas purification catalyst becomes insufficient and purification capacity deteriorates. For this reason, an exhaust gas purification system having characteristics, in which a catalyst reaches an activating temperature immediately after the start of an engine and the catalyst having reached the activating temperature is hardly cooled and maintains catalytic activity even when low-temperature exhaust gas flows in, is required.
Accordingly, a system using an electrically heated catalyst (EHC) has been proposed in the past as an exhaust gas purification system that can perform uniform heating (for example, see Patent Document 1). This system is a system that includes electrodes provided on a honeycomb structure formed of a conductive ceramics and raises the temperature of a catalyst up to an activating temperature before the start of an engine by making the honeycomb structure generate heat by the flow of current.
Further, a heating device, in which electric heaters (resistance heating heaters) are disposed so as to surround the circumferential wall of a honeycomb structure and which transfers heat to a cell structure provided in the honeycomb structure by heating the surface of the circumferential wall of the honeycomb structure, also has been proposed as an exhaust gas purification device that can perform uniform heating (for example, see Patent Document 2).
[Patent Document 1] JP-A-2010-229976
[Patent Document 2] JP-A-2012-241548
Patent Document 2 has disclosed that an electrical heater (resistance heating heater) itself is replaced when an electrical heating wire embedded in a heat-insulation material is disconnected. However, since the honeycomb structure and a metal case provided around the electric heater are fixed to each other by welding or the like, it is not easy to replace the electric heater. Further, when disconnection occurs only in one electric heater among the plurality of electric heaters disposed so as to surround the outer wall of the honeycomb structure and the portion where disconnection occurs is not heated, large distribution in the heating of the honeycomb structure is generated. For this reason, there is a possibility that the breakage of the honeycomb structure, and the like may occur.